CNA-BUG-117: The SdlRenderer constructor maps any positive swap interval to 1, so a device constructed with PresentInterval::Two runs at interval 1 until the next reset

CNA snapshot 009d40f5  ·  Known Issues › Current bugs  ·  source links pinned to 009d40f5

The constructor calls SDL_SetRenderVSync(renderer, swapInterval > 0 ? 1 : 0), while SetSwapInterval (Task 713) passes 2 through and falls back only if the driver refuses it.

Identifier

CNA-BUG-117

Category

Bug

Subsystem

Graphics & renderers

Status

Open

Verified against

CNA 009d40f5 (009d40f5dd085c4e674d3479675fac84b12b3e0a)

Severity

Low (a triage suggestion, not a project priority)

Evidence basis

Source-verified: read at TARGET, not executed

Tests touching this area

Yes: see Current tests

Affected contract

GraphicsDevice construction with PresentationParameters.PresentationInterval = Two on SDL_RENDERER

Expected behaviour

CNA's own Task 713 fix in SetSwapInterval establishes the contract: interval 2 is forwarded as 2 (every second vertical refresh), with a fallback to 1 only when SDL rejects it.

Actual behaviour at TARGET

SdlRenderer.cpp's constructor still has the pre-fix mapping, with a stale comment claiming that SDL_SetRenderVSync supports only 0 and 1. A GraphicsDevice constructed with PresentInterval::Two therefore starts at interval 1; the Game path is unaffected in practice because GraphicsDeviceManager's Reset forwards the interval again through SetSwapInterval (and the manager only ever requests One or Immediate).

Source locations

• modules/renderers/sdl-renderer/src/SdlRenderer.cpp — SdlRenderer constructor SDL_SetRenderVSync call and SdlRenderer::SetSwapInterval

Evidence

Checked by reading the named sources at 009d40f5; nothing was built or executed for this entry.

Focused reproduction

No focused reproduction is known. Nothing has been invented here; the evidence above is what exists.

Current tests

sdlrenderer_presentinterval_test.cpp checks forwarding through SetSwapInterval, not the constructor.

Regression test

A test that constructs a device with PresentInterval::Two and queries SDL_GetRenderVSync.

Blast radius

Directly constructed GraphicsDevices (tools, embedding) that request Two on SDL_RENDERER.

Workaround

Call Reset or SetPresentationParameters after construction.